The field of data communications typically uses modems, or communication devices, to convey information from one location to another. Digital Subscriber Line (DSL) technology now enables communications devices to communicate large amounts of data. This communication scheme adheres generally to a model, known as the Open Systems Interconnect (OSI) Seven-Layer model. This model specifies the parameters and conditions under which information is formatted and transferred over a given communications network. A general background of the OSI seven layer model follows.
In 1978, a framework of international standards for computer network architecture known as OSI (Open Systems Interconnect) was developed. The OSI reference model of network architecture consists of seven layers. From the lowest to the highest, the layers are: (1) the physical layer; (2) the datalink layer; (3) the network layer; (4) the transport layer; (5) the session layer; (6) the presentation layer; and (7) the application layer. Each layer uses the layer below it to provide a service to the layer above it. The lower layers are implemented by lower level protocols which define the electrical and physical standards, perform the byte ordering of the data, and govern the transmission and error detection and correction of the bit stream. The higher layers are implemented by higher level protocols which deal with, inter alia, data formatting, terminal-to-computer dialogue, character sets, and sequencing of messages.
Layer 1, the physical layer, controls the direct host-to-host communication between the hardware of the end users' data terminal equipment (e.g., a modem connected to a PC).
Layer 2, the datalink layer, generally fragments the data to prepare it to be sent on the physical layer, receives acknowledgment frames, performs error checking, and re-transmits frames which have been incorrectly received.
Layer 3, the network layer, generally controls the routing of packets of data from the sender to the receiver via the datalink layer, and it is used by the transport layer. An example of the network layer is Internet Protocol (IP) which is the network layer for the TCP/IP protocol widely used on Ethernet networks. In contrast to the OSI seven-layer architecture, TCP/IP (Transmission Control Protocol over Internet Protocol) is a five-layer architecture which generally consists of the network layer and the transport layer protocols.
Layer 4, the transport layer, determines how the network layer should be used to provide a point-to-point, virtual, error-free connection so that the end point devices send and receive uncorrupted messages in the correct order. This layer establishes and dissolves connections between hosts. It is used by the session layer. TCP is an example of the transport layer.
Layer 5, the session layer, uses the transport layer and is used by the presentation layer. The session layer establishes a connection between processes on different hosts. It handles the creation of sessions between hosts as well as security issues.
Layer 6, the presentation layer, attempts to minimize the noticeability of differences between hosts and performs functions such as text compression and format and code conversion.
Layer 7, the application layer, is used by the presentation layer to provide the user with a localized representation of data which is independent of the format used on the network. The application layer is concerned with the user's view of the network and generally deals with resource allocation, network transparency and problem partitioning.
Existing digital subscriber line (DSL) devices operating in the full-duplex mode conduct equalizer training and coefficient determination using previously stored channel operating parameters determined by operations performed in the datalink layer (layer 2). For example, U.S. Pat. No. 4,621,366 discloses a modem that acquires, stores and reinitializes the modem equalizer using channel operating parameters determined during an initial training sequence. For a subsequent transmission, the modem uses the stored coefficients and parameters during a shortened training sequence. While this operation takes place in layer one of the OSI seven layer model, the aforementioned modem only uses the equalizer's mean-square-error vector to determine the probability of erroneous equalizer updating. Various channel conditions may cause the modem's equalizer to track inappropriately. By using only the modem's mean square error vector to determine the probability of erroneous equalizer updating, existing modems fail to take advantage of the layer two framing and frame check sequence available to a device's digital signal processor (DSP) in layer one of the OSI seven layer model.
In a multipoint communication environment including a control device and a plurality of remote devices, each device includes a transmitter and a receiver. Each device uses messages incorporating a protocol which includes the receiving device's address and a poll bit. The poll bit is set by the control device to indicate an expected response from a particular remote device. During an initial start up sequence, reception of a relatively long training sequence is necessary before data communication can proceed. The receiver parameters, including adaptive equalizer coefficients, for each remote device that has successfully completed the aforementioned lengthy training sequence are stored in a memory located within the control device. The control device will store the parameters for each remote device in a memory location dedicated to that particular remote device.
During subsequent transmissions, a relatively short training sequence, which synchronizes the control device receiver and identifies the transmitting remote device is used. During the reception of the subsequent message, parameters within the control device's equalizer, and other adaptive devices parameters, are adaptive and are modified to compensate for any changes in the channel characteristics.
Therefore, it would be desirable to provide a more robust technique for updating adaptive receiver parameters by allowing a DSP in a control device to use the layer two error detection results to decide whether the new adaptive parameters, available during the shortened training period, should be saved and used or discarded in favor of the last known good parameters.